Buffett, 80, has long advised Post Co.'s chairman and chief executive Donald E. Graham on the financial stewardship of the company. He was also an adviser and close personal friend of Graham's mother and predecessor as chairman, the late Katharine Graham.

Berkshire Hathaway is the largest shareholder in the Post, with 21 percent of the common stock, and Buffett said in an interview that he does not intend to alter his stake. The Graham family controls the company through its ownership of separate class of stock.

"It won't change at all," Buffett said. "I'll never back away from that statement." He predicted that his obituary, which he said he hoped would not be published anytime soon, would say that he owned the same number of shares of the Post Co.

But he said that "the newspaper business will be tougher and tougher and tougher, and it is already plenty tough." While he said that the newspaper was "the centerpiece of the Post Co., that doesn't mean that it will earn the most money."

Buffett said that he expected that the company would continue to rely on a number of other businesses.

The Berkshire Hathaway chairman said that he was leaving the Post board because of other travel commitments linked to Berkshire Hathaway acquisitions abroad. He noted that he has given up his seats on other corporate boards, including the Coca-Cola Co. board last year. "I have $12 billion worth of its stock," he said. "I'll never lose my attachment to it, but it was six days in Atlanta."

"I've got lots of energy but I am 80," he said. "I love this place, but it's gotten to the point where I only have 365 days in a year."

Earlier, in a prepared statement, Donald Graham said, "For most of the last 37 years, we've been privileged to have on our board perhaps the best adviser any company could have had throughout that period."

The legendary investor, chairman of the finance committee of The Post Co. board, has served nearly 26 years on the board, first from 1974 to 1986 and then from May 1996 to the present.

Graham said he will still regularly seek advice from Buffett. "Warren has encouraged us to continue to consult him on Company matters and with the encouragement of our board, calls to the 402 area code will not be decreasing," Graham said in the statement, alluding to Buffett's base of operations in Omaha, Neb.

Buffett said in the interview that he would be available. "Now they'll just get my advice cheaper," he said.

Shares of The Post, which had risen earlier on news of a boost in the annual dividend, fell back on news of Buffett's departure.

Buffett has been paying increasing attention to grooming possible successors at Berkshire Hathaway, and he also recently relinquished his board seat at the Coca-Cola Co. His son Howard G. Buffett replaced him there.

Buffett provided a steady financial hand at the Post Co. when Katharine Graham needed one, and he has supported the diversification of the company into Kaplan, the education division that has become the company's largest unit. Recently Kaplan and other for-profit education firms have been hit with allegations about misleading marketing, which has prompted the Education Department to consider tougher regulation of the industry.

Asked about the criticism of Kaplan, Buffett said, "If it deserves to grow, it'll grow." He added, "we're in the early stages of the for-profit industry."

Buffett has been pessimistic about the state of the newspaper industry for some time. In his annual letter to his company's shareholders in 2007, Buffett wrote that "fundamentals are definitely eroding in the newspaper industry" and warned that "the skid will almost certainly continue."